PUTREFACTION PRODUCTS. 169 



what more concentrated than that mentioned above and if heat is 

 used. Under these conditions the blue indole compound ultimately 

 forms as fine acicular crystals which rise to the surface. 



If w r e do not wait for the production of the crystalline body but as 

 soon as the blue color forms, shake the aqueous solution with chlor- 

 oform, the blue color disappears from the solution and the chloro- 

 form assumes a pinkish-red hue. This is a distinguishing feature 

 of the indole reaction and facilitates the differentiation of indole 

 from other bodies which yield a similar blue color. 



2. Konto's Reaction. Distil the solution to be tested until only 

 one-third of the original solution remains. Make the distillate al- 

 kaline with sodium hydroxide and distil again in order to separate 

 the indole from the phenol, the latter remaining in the residue. In- 

 asmuch as this second distillate generally contains a large amount 

 of ammonia it should be acidified with dilute sulphuric acid and 

 again distilled. To i c.c. of this ammonia-free distillate in a test- 

 tube add 3 drops of a 40 per cent solution of formaldehyde and 

 i c.c. of concentrated sulphuric acid. Now agitate the mixture 

 and note the appearance of a violet red color if a trace of indole 

 is present. The test is said to serve for the detection of indole 

 when present in a dilution of i 1700,000. 



Skatole gives a yellow or brown color under the above conditions. 



3. Cholera-red Reaction. To a little of the residue in a test- 

 tube add one-tenth its volume of a 0.02 per cent solution of potas- 

 sium nitrite and mix thoroughly. Carefully run concentrated sul- 

 phuric acid down the side of the tube so that it forms a layer at 

 the bottom. Note the purple color. Neutralize with potassium 

 hydroxide and observe the production of a bluish-green color. 



4. Legal's Reaction. To a small amount of the residue in a 

 test-tube add a few drops of a freshly prepared solution of sodium 

 nitroprusside, Na 2 Fe(CN) 5 NO + 2H 2 O. Render alkaline with 

 potassium hydroxide and note the production of a violet color. If 

 the solution is now acidified with glacial acetic acid the violet is 

 transformed into a blue. 



5. Pine Wood Test. Moisten a pine splinter with concentrated 

 hydrochloric acid and insert it into the residue. The wood as- 

 sumes a cherry-red color. 



6. Nitroso-indole Nitrate Test. Acidify some of the residue 

 with nitric acid, add a few drops of a potassium nitrite solution and 

 note the production of a red precipitate of nitroso-indole nitrate. If 

 the residue contains but little indole simply a red coloration will 



